1. Field of Invention
The invention relates to an antenna and, in particular, to a dual-band antenna.
2. Related Art
The prosperous development in wireless transmission has brought us various kinds of multi-frequency transmission products and technologies. Many new products are built in with the function of wireless transmissions. The antenna is an important element in a wireless transmission system to emit and receive electromagnetic (EM) wave energy. Without the antenna, the wireless transmission system will not be able to emit and receive data. Therefore, the antenna is indispensable for wireless transmissions. Besides fitting to the product shape and enhancing transmissions, using an appropriate antenna can further reduce the product cost.
Commonly used standards of the bandwidths include IEEE 802.11 and the hottest Bluetooth communications (802.15.1). The Bluetooth technology works in the 2.4 GHz band. The 802.11 standard is further divided into 802.11a, 802.11b, 502.11g and 802.11n, defined for the 5 GHz band and the 2.4 GHz band, respectively.
The wireless LAN apparatuses, such as the wireless network card and the access point, can sufficiently simplify the set-up of the network hardware. In addition, since the wireless LAN apparatuses are portable, they become more convenient. In order to enhance-the transmission ability, the wireless LAN apparatus is usually equipped with dual-band or multi-band transmission function, so that it can switch between different modes for receiving or transmitting desired data.
However, it is time consumption to design antennas with different bands, and the antennas with different bands may occupy large area or space. Accordingly, the dual-band antenna, which can operate in two different bands, is developed. In addition, since the electronic devices are manufactured smaller, the size of the antennas is also requested to be decreased. Therefore, it is an important subject to decrease the size of the antenna.